1. Field of the Invention
The present invention relates to improving the light fastness of organic substrate materials and more particularly to improving the light fastness of organic compounds useful as dyestuffs. The present invention is particularly directed to improving the light fastness of organic substrate materials occurring in photographic materials, e.g., color films, prints, etc.; in colored polymers useful as agricultural vinyl cover sheets, umbrellas, tents, etc.; of fluorescent whitening agents; and dyed textiles, etc.
2. Description of the Prior Art
It is commonly accepted that organic substances such as, for example, organic dyes tend to fade upon exposure to light. Extensive studies are being carried out in various technical fields such as in printing inks, textile dyeing as well as in color photography, in an effort to improve the light fastness of the organic dyes.
The present invention is advantageously used to improve the light fastness of such organic substrates.
In the following description, the term "organic substrate material" or "organic substrate" means a material appearing colored to the human eye under the illumination of sunlight, including not only those compounds having absorption peaks in the visible region of spectrum, but those with absorption peaks which lie in the infrared region or in the ultraviolet region, such as optical whitening agent. In other words, the organic substrate materials of the present invention include those organic colorants having the absorption peaks at the wavelength of from 300 to 800 nm.
In the present specification, the term "dye" or "dyestuff" means an organic material which appears colored to the human eye under the illumination of sunlight.
In the present specification, the term "light" conceptually includes electromagnetic radiation with wavelengths up to about 800 nm, thus including ultraviolet rays below 400 nm, visible light of from about 400 nm to about 700 nm and infrared radiation of from about 700 to about 800 nm.
It is well known that organic substrate materials such as, for example, dyes or coloring agents tend to fade by the action of light; and a number of publications dealing with the methods of suppressing tendency or improving the light fastness of such materials are known. For example, U.S. Pat. No. 3,432,300 discloses that the light fastness of organic compounds such as indophenol, indoaniline, azo and azomethine dyes against visible and UV light can be improved using phenol derivatives containing a condensed heterocyclic structure. "The Theory of the Photographic Process" authored by Mees et al (3rd edition-1967) teaches in Chapter 17, that silver halide color photographic materials generally give rise to axomethine or indoaniline dyes resulting upon the reaction of the oxidation product from an aromatic primary amine developing agent with a color coupler. Various patents also describe how to improve the stability to light of color photographic images thus obtained. Compounds which are effective for the improvement of the light fastness of the co-existing dye include, for example, the hydroquinone derivatives set forth in U.S. Pat. Nos. 2,360,290, 2,418,613, 2,675,314, 2,701,197, 2,704,713, 2,728,659, 2,732,300, 2,735,765, 2,710,801 and 2,816,028 and Brit. Pat. No. 1,363,921, etc., gallic acid derivatives set forth in U.S. Pat. Nos. 3,457,079 and 3,069,262, Japan. Pat. Appl. (OPI) No. 13,496/1968, etc., p-alkoxyphenols set forth in U.S. Pat. Nos. 2,735,765 and 3,698,909, chroman and coumarane derivatives set forth in U.S. Pat. Nos. 3,432,300, 3,574,626, 3,698,909, 3,573,050 and 4,015,990, etc. These compounds are effective in preventing fading or discoloration of dye images to a certain extent, but are not as satisfactory as would be desired.
Brit. Pat. No. 1,451,000 discloses that the stability to light of organic substrate materials is enhanced by the use of azomethine quenching compounds which have their absorption peaks at a longer wavelength than the substrate material. Unfortunately, the azomethine quenching compound is colored itself and adversely affects the color hue of the substrate material. Metal chelates can be used to prevent the degradation of polymeric materials caused by the action of light as is described in the following literature; J. P. Guillory & R. S. Becker, J. Polym. Sci., Polym. Chem. Ed., 12, 993 (1974), and R. P. R. Ranaweera & G. Scott, J. Polym. Sci., Polym. Let. Ed., 13, 71 (1975), etc. Stabilization of dyes against light by the use of metal chelates is also set forth in U.S. Pat. No. 4,050,938, Published Japanese Patent Application (OPI) No. 87,649/1975 and Research Disclosure 15162 (1976). However, the disclosed metal chelates do not exhibit a satisfactory fade preventing effect and when the metal chelates are employed in a photographic emulsion for practical use the disclosed metal chelates desensitize the silver halide probably due to an undesirable interaction with silver. Also the metal chelates exhibit an undesirably poor solubility in organic solvents. The latter property limits the working concentration of such a chelate to amounts which are too low to provide sufficient fade prevention. Moreover, these chelates cannot be present in a high concentration since they themselves are colored and they adversely affect the color hue and the color purity of the dyes.
Furthermore, heretofore agents suitable for preventing the fading of cyan dyes have not been known.